In 3GPP (3rd Generation Partnership Project) which is a project aiming to standardize a mobile communication system, the introduction of Device-to-Device (D2D) communication is discussed as a new function after Release 12 (see Non Patent Literature 1).
The D2D proximity service is a service enabling direct communication within a synchronization cluster consisting of a plurality of synchronized user terminals without passing through a network. The D2D proximity service includes a discovery process (Discovery) in which a proximal terminal is discovered and a communication process (D2D communication) in which direct communication is performed.